Abaixo está uma instrução que descreve uma tarefa de geração de SQL, combinada com uma entrada que fornece mais contexto sobre os esquemas de tabela disponíveis. Escreva o código SQL que responda adequadamente à solicitação
 ###Instrução: Quem é o artista original com um tema de N/A?
 ###Tabelas: CREATE TABLE historical_premiers (historical_premiers_id AUTO_INCREMENT PRIMARY KEY, Rank: INT, State: VARCHAR, Premier: VARCHAR, Party: VARCHAR, Assumed office: VARCHAR, Left office: VARCHAR, TOTAL Time in office: VARCHAR) CREATE TABLE composition_of_the_14th_seanad (composition_of_the_14th_seanad_id AUTO_INCREMENT PRIMARY KEY, Administrative Panel INT, Agricultural Panel INT, Cultural and Educational Panel INT, Industrial and Commercial Panel INT, Labour Panel INT, National University of Ireland INT, University of Dublin INT, Nominated by the Taoiseach INT, Total INT) CREATE TABLE premierships_8_62 (premierships_8_62_id AUTO_INCREMENT PRIMARY KEY, Year INT, Opponent VARCHAR, Competition VARCHAR, Score VARCHAR, Venue VARCHAR, Attendance VARCHAR) CREATE TABLE 2010_team (2010_team_id AUTO_INCREMENT PRIMARY KEY, Player VARCHAR, Position VARCHAR, School VARCHAR, Hometown VARCHAR, College VARCHAR) CREATE TABLE performances_results (performances_results_id AUTO_INCREMENT PRIMARY KEY, Week # VARCHAR, Theme VARCHAR, Song choice VARCHAR, Original artist VARCHAR, Order # VARCHAR, Result VARCHAR)  
SELECT Original artist FROM performances_results WHERE Theme = N/A